Publications

Keratinocytes require abundant cholesterol for cutaneous permeability barrier function; hence, the regulation of cholesterol homeostasis is of great importance. ABCA1 is a membrane transporter responsible for cholesterol efflux and plays a pivotal role in regulating cellular cholesterol levels. We demonstrate that ABCA1 is expressed in cultured human keratinocytes (CHKs) and murine epidermis. Liver X receptor (LXR) activation markedly stimulates ABCA1 mRNA and protein levels in CHKs and mouse epidermis. In addition to LXR, activators of peroxisome proliferator-activated receptor (PPAR)alpha, PPARbeta/delta, and retinoid X receptor (RXR), but neither PPARgamma nor retinoic acid receptor, also increase ABCA1 expression in CHKs. Increases in cholesterol supply induced by LDL or mevalonate stimulate ABCA1 expression, whereas inhibiting cholesterol synthesis with statins or cholesterol sulfate decreases ABCA1 expression in CHKs. After acute permeability barrier disruption by either tape-stripping or acetone treatment, ABCA1 expression declines, and this attenuates cellular cholesterol efflux, making more cholesterol available for regeneration of the barrier. In addition, during fetal epidermal development, ABCA1 expression decreases at days 18-22 of gestation (term = 22 days), leaving more cholesterol available during the critical period of barrier formation. Together, our results show that ABCA1 is expressed in keratinocytes, where it is negatively regulated by a decrease in cellular cholesterol levels or altered permeability barrier requirements and positively regulated by activators of LXR, PPARs, and RXR or increases in cellular cholesterol levels.

BACKGROUND

Lipoprotein Lipase (LPL), a key enzyme in lipid metabolism, catalyzes the hydrolysis of triglycerides (TG) from TG-rich lipoproteins, and serves a bridging function that enhances the cellular uptake of lipoproteins. Abnormalities in LPL function are associated with pathophysiological conditions, including familial combined hyperlipidemia (FCH). Whereas two LPL susceptibility alleles were found to co-segregate in a few FCH kindred, a role for common, protective alleles remains unexplored. The LPL Ser447Stop (S447X) allele is associated with anti-atherogenic lipid profiles and a modest reduction in risk for coronary disease. We hypothesize that significant depletion of the 447X allele exists in combined hyperlipidemia cases versus controls. A case-control design was employed. The polymorphism was assessed by restriction assay in 212 cases and 161 controls. Genotypic, allelic, and phenotypic associations were examined.

RESULTS

We found evidence of significant allelic (447Xcontrol: 0.130 vs. 447Xcase: 0.031, chi2 = 29.085; 1df; p < 0.001) and genotypic association (SS: 0.745 vs. 0.939, and SX+XX: 0.255 vs. 0.061) in controls and cases, respectively (chi2 = 26.09; 1df; p < 0.001). In cases, depletion of the 447X allele is associated with a significant elevation in very-low-density lipoprotein cholesterol (VLDL-C, p = 0.045). Consonant with previous studies of this polymorphism, regression models predict that carriers of the 447X allele displayed significantly lower TG, low-density lipoprotein cholesterol (LDL-C) and TG/high-density lipoprotein cholesterol (HDL-C) ratio.

CONCLUSION

These findings suggest a role for the S447X polymorphism in combined hyperlipidemia and demonstrate the importance of evaluating both susceptibility and protective genetic risk factors.

Prostasin, a trypsinlike serine peptidase, is highly expressed in prostate, kidney, and lung epithelia, where it is bound to the cell surface, secreted, or both. Prostasin activates the epithelial sodium channel (ENaC) and suppresses invasion of prostate and breast cancer cells. The studies reported here establish mechanisms of membrane anchoring and secretion in kidney and lung epithelial cells and demonstrate a critical role for prostasin in regulating epithelial monolayer function. We report that endogenous mouse prostasin is glycosylphosphatidylinositol (GPI) anchored to the cell surface and is constitutively secreted from the apical surface of kidney cortical collecting duct cells. Using site-directed mutagenesis, detergent phase separation, and RNA interference approaches, we show that prostasin secretion depends on GPI anchor cleavage by endogenous GPI-specific phospholipase D1 (Gpld1). Secretion of prostasin by kidney and lung epithelial cells, in contrast to prostate epithelium, does not depend on COOH-terminal processing at conserved Arg(322). Using stably transfected M-1 cells expressing wild-type, catalytically inactive, or chimeric transmembrane (not GPI)-anchored prostasins we establish that prostasin regulates transepithelial resistance, current, and paracellular permeability by GPI anchor- and protease activity-dependent mechanisms. These studies demonstrate a novel role for prostasin in regulating epithelial monolayer resistance and permeability in kidney epithelial cells and, furthermore, show specifically that prostasin is a critical regulator of transepithelial ion transport in M-1 cells. These functions depend on the GPI anchor as well as the peptidase activity of prostasin. These studies suggest that cell-specific Gpld1- or peptidase-dependent pathways for prostasin secretion may control prostasin functions in a tissue-specific manner.

BACKGROUND

Tissue engineering approaches involving the direct transplantation of cardiac patches have received significant attention as alternative methods for the treatment of damaged hearts. In contrast, we used cardiomyocyte sheets harvested from temperature-responsive culture dishes to create pulsatile myocardial tubes and examined their in vivo function and survival.

METHODS AND RESULTS

Neonatal rat cardiomyocyte sheets were sequentially wrapped around a resected adult rat thoracic aorta and transplanted in place of the abdominal aorta of athymic rats (n=17). Four weeks after transplantation, the myocardial tubes demonstrated spontaneous and synchronous pulsations independent of the host heartbeat. Independent graft pressures with a magnitude of 5.9+/-1.7 mm Hg due to their independent pulsations were also observed (n=4). Additionally, histological examination and transmission electron microscopy indicated that the beating tubes were composed of cardiac tissues that resemble the native heart. Finally, when myocardial tubes used for aortic replacement were compared with grafts implanted in the abdominal cavity (n=7), we observed significantly increased tissue thickness, as well as expression of brain natriuretic peptide, myosin heavy chain-alpha, and myosin heavy chain-beta.

CONCLUSIONS

Functional myocardial tubes that have the potential for circulatory support can be created with cell sheet engineering. These results also suggest that pulsation due to host blood flow within the lumen of the myocardial tubes has a profound effect on stimulating cardiomyocyte hypertrophy and growth. These results demonstrate a novel approach for the future development of engineered cardiac tissues with the ability for independent cardiac assistance.

BACKGROUND

Altered conduction is associated with increased atrial fibrillation (AF) vulnerability in canine models of chronic mitral regurgitation (MR) and heart failure (HF). Rotigaptide (ZP123) augments gap junction conductance, improving cell-to-cell coupling. We studied the effects of rotigaptide on atrial conduction and AF vulnerability in the canine MR and HF models.

METHODS AND RESULTS

Twenty-one dogs in 3 groups were studied: control (n=7), chronic MR induced by mitral avulsion (n=7), and HF induced by ventricular tachypacing (n=7). Epicardial mapping of both atria was performed with a 512-electrode array at baseline and at increasing rotigaptide doses (10, 50, and 200 nmol/L). Conduction velocity increased in both atria in control animals and MR animals (maximum percentage increase: 24+/-5%, 38+/-6% [P<0.001, <0.001] in the left atrium and 19+/-9%, 18+/-3% [P<0.001, <0.001] in the right atrium). Conduction velocity did not change in the left atrium of the HF group and increased minimally in the right atrium (3+/-3%, 17+/-5% [P=NS, P=0.001]). AF duration was increased at baseline in MR and HF animals (control: 16+/-25 seconds, MR: 786+/-764 seconds, HF: 883+/-684 seconds; P=0.013). At 50 nmol/L of rotigaptide, duration of AF markedly decreased in the MR animals (96% reduction, P<0.001), reducing AF duration to that of control animals (control: 9+/-11 seconds, MR: 14+/-16 seconds, HF: 1622+/-355 seconds; P=0.04).

CONCLUSIONS

Gap junction modulation with rotigaptide reduces AF vulnerability in a canine MR model of AF to a level similar to control animals but does not affect AF vulnerability in the canine HF model. This may be a novel therapeutic target in some forms of AF.

A 15-year-old girl with perinatal HIV-1 infection has remained asymptomatic with undetectable plasma HIV-1 viremia for more than 5 years after discontinuing all antiretroviral therapy. Viral sequence analysis of proviral HIV-1 DNA revealed no evident fitness-attenuating deletions or mutations. This subject exhibited an unusually robust HIV-specific T-cell response, with an intact CD4+ T cell-proliferative response to HIV-1 antigens. In addition, the subject was found to be heterozygous for the 32-bp deletion in the CCR5 gene, which encodes the primary coreceptor for HIV-1 entry into cells. This mutation mediates profound resistance to HIV infection in homozygotes and has been associated with delayed disease progression in heterozygotes after both horizontal and vertical HIV-1 infection. Although adults with long-term nonprogressive HIV disease have been studied at length, there is no prior description in the literature of a perinatally HIV-infected child whose plasma HIV-1 viremia is controlled to undetectable levels in the absence of antiretroviral therapy.